Full moon may disrupt sleep, study says

Elizabeth Landau |
7/29/2013, 6:14 a.m.

CNN  You don't have to be a werewolf to feel restless when the full moon rises.

A new study in the journal Cell Biology suggests that people tend to get lower quality sleep around the time of full moons, snoozing an average of 20 minutes less than they do during a new moon.

"If you ask people, at least in Switzerland, about 40% report feeling the moon during sleep, or they blame the full moon for bad sleep," said lead study author Christian Cajochen of the Psychiatric Hospital of the University of Basel in Switzerland.

That's why he and his colleagues decided to investigate.

The study

The study included 33 healthy volunteers, between ages 20 and 74. Participants slept under strictly controlled conditions in a laboratory with no windows, so they had no way of seeing the moon. They stayed in the laboratory for 3½ days. Humidity and temperature were controlled.

Neither the participants nor the researchers knew, at the time of the experiment, that the phase of the moon would become part of the study. This decision reduced any bias that either group may have introduced regarding the moon -- but also presented the drawback that the study didn't look at all phases of the moon's cycle.

The data come from an experiment done 10 years ago; Cajochen and colleagues didn't analyze the results in terms of lunar patterns until several years after they did the study and waited to publish until now.

The results

The full moon was associated with a 20-minute reduction of total sleep time, the study authors found.

Researchers also found that it took about five minutes longer for participants to fall asleep around a full moon than around a new moon. Deep sleep was, on average, 30% decreased around the time of a full moon.

People sleeping in the lab nearer to the day of a full moon also had lower evening levels of melatonin, a hormone important to circadian rhythm that drives the body's cycles of day and night and, therefore, wakefulness and sleep.

"We have evidence that the distance to the nearest full-moon phase significantly influences human sleep and evening melatonin levels when measured under strictly controlled laboratory conditions, where factors such as light and personal moon perception can be excluded," the study authors wrote.

Study limitations

The number of participants in the study was small so the results may not apply to wider population. Also, the researchers didn't control what volunteers were exposed to in the week before the study; their individual environments could have influenced their sleep habits.

Generally, the methods and analyses in this experiment are solid, said Philip Gehrman, assistant professor of psychiatry at the University of Pennsylvania, who was not involved in the study.

In graduate school, Gehrman analyzed data about the sleep habits of older adults with Alzheimer's disease in nursing homes to see if lunar cycles had an effect. He didn't find one, but "the nurses would swear that the patients became more agitated and slept worse during a full moon," he told CNN in an e-mail.